The present invention relates to a polyolefin alloy with improved surface hardness and scratch resistance, and processes for producing same. More specifically, the invention relates to a polyolefin alloy on the basis of a polypropylene material, a functionalized polypropylene material, a mineral, an amorphous silica gel and optionally an ethylene/propylene/polyene terpolymer (EPDM), as well as processes for producing said polyolefin alloy.
Various techniques for increasing the scratch resistance of polyolefin materials are previously known, i.a. addition of silica materials. Thus, JP 1318051 (Toray Silicone KK) discloses polyolefins which for this purpose have been modified with a filler on silica basis. Said filler may have been surface treated with silane type compounds. However, the disclosed polyolefins are not alloys and no fatty acid amide-treated silica gel is used in the material. JP 1104637 (Showa Denko KK) discloses materials on a polypropylene basis to which silica/alumina spheroids and a polypropylene material functionalized with carboxylic acid or carboxylic anhydride have been added. These materials also contains no fatty acid amide-treated silica gel.
It has now been found that when a functionalized polypropylene material and an amorphous, fatty acid amide-modified silica gel are incorporated into certain polyolefin materials having a mineral content, the scratch resistance of the material is substantially improved, with retention of the impact strength and the thermal shape stability (HDTA) of the material.
Thus, the invention provides a new polyolefin alloy having improved surface hardness and scratch resistance, and having a melt index MI in the range of 0.1-50 g/10 min at 230.degree. C./2.16 kg, particularly in the range of 3 to 40 g/10 min at 230.degree. C./2.16 kg. The polyolefin alloy is characterized in that it is constituted by a blend of:
(A) 40 to 80% by weight of a polypropylene material consisting of a polypropylene homopolymer or a copolymer of propylene with ethylene and/or butadiene, which polypropylene material may have a content of polymerized ethylene and/or butadiene units of 5 to 35 mole % and has a molecular weight Mw of 100,000 to 300,000 and a melt index MI of 0.1 to 20 g/10 min at 230.degree. C./2.16 kg, PA1 (B) 1 to 10% by weight of a functionalized polypropylene material consisting of a grafted polypropylene homopolymer or copolymer of propylene with ethylene and/or butadiene, having a degree of grafting of 0.2 to 10% by weight, PA1 (C) 1 to 50% by weight of a mineral, having a mean particle size of about 2.5 .mu.m and a maximum particle size of about 20 .mu.m, and being surface-treated with 0.2 to 5% by weight of aminosilane, PA1 (D) 1 to 15% by weight of amorphous fatty acid-treated silica gel, comprising 25 to 75% by weight of silica and 75 to 25% by weight of fatty acid amide, PA1 (E) 0 to 40% by weight of an ethylene/propylene/polyene terpolymer (EPDM) having a melt index MI in the range of 1 to 10 g/10 min at 230.degree. C./2.16 kg and a Shore D hardness of 30 to 70.
EP-A-0 567 058 (Hirano et al.) discloses compositions having improved elasticity, peeling strength and recoating properties, comprising a polypropylene, an ethylene/.alpha.-olefin copolymer elastomer, and a modified polyolefin having a functional group in either or both ends thereof, as well as certain substituted amines/amides. In addition thereto, the compositions can also contain various additives, among which talc is mentioned. Said compositions of EP-A-0 567 058 do not, however, contain the combination of a functionalized polypropylene material of the same kind as component (B) of the polyolefin alloy of the present invention, with a mineral having been surface-treated with an aminosilane, and a fatty acid-treated silica gel, and they do not suggest any improvement of the scratch resistance.
U.S. Pat No. 4,675,122 (Luers et al.) teaches a combined antiblocking agent and lubricant concentrate based on polyolefin, which contains diatomaceous earth, precipitated silica and/or silica gel as the antiblocking agent, and one more more amides of unsaturated C.sub.18 -C.sub.22 fatty acids. No mention is made of any improvement of the scratch-resistance. Also, it could not be considered to be near at hand to combine the teaching of U.S. Pat No. 4,675,122 with the teaching of the above-discussed EP-A-0 567 058, which also does not mention scratch-resistance.
EP-A-0 297 693 (McKinney et al.) teaches a composition comprising an intimate mixture of at least one ethylene interpolymer with acrylic acid, methacrylic acid or an ionomer of either of said acids and a slip-enhancing amount of a secondary fatty acid amide. The composition may also contain small amounts of finely divided inorganic materials such as silica and talc. The aim of the invention of EP-A-0 297 693 is to improve the slip and/or block characteristics of the ethylene interpolymers. No mention is made of any improvement of the scratch-resistance. Even though said EP-A-0 297 693 is disclosing compositions in which silica may be used, and will come into contact with fatty acid amide, it is not question there of any fatty acid-treated silica gel comprising 25-75% by weight of silica and 75-25% by weight of fatty acid amide as in the polyolefin alloy of the present invention. To the extent a finely inorganic material is used in the composition of EP-A-0 297 693, no surface treatment thereof with aminosilane is mentioned, neither is there any mention of any functionalized polypropylene material. A similar composition is disclosed in EP-A-0 257 803 (Yamada et al.), comprising an ethylene/methyl methacrylate copolymer, a slip agent which may be a fatty acid amide, and a small amount (0.01-0.1 % wt) of an inorganic filler, which may be a silica or a talc. The composition is used to produce peelable protective films with low peeling strength for wrapping around e.g. rubbery articles having a tacky surface. Neither EP-A-0 257 803 nor EP-A-0 297 693 suggests the polyolefin alloy of the present invention having improved surface hardness and scratch-resistance.
U.S. Pat. No. 5,286,791 (De Nicola et al.) discloses a filled composition having improved flexural modulus and impact strength, comprising a propylene polymer material, a propylene polymer material grafted with one or more vinyl monomers, and a rubber component. As filler, the composition may contain i.a. talc and silica, and column 3, lines 25-37, of the patent indicates that the filler may be coated with an organic compound. However, the patent does not suggest any fatty acid amide-treated silica gel in combination with an aminosilane-treated mineral and there is no suggestion in said patent that any such combination would improve the surface hardness and scratch-resistance of a polyolefin alloy as defined according to the present invention.